If a service adviser calls me while my truck is in the shop and inform me I need additional work, I usually ask them to save the old (worn) parts for me to inspect when I pick up the truck. Granted they could have a bunch of old parts lying around to show you. Another option is to tell them you need your truck back ASAP and you'll schedule an appointment in the near future. In your case with the rear seal, I would have told them to top off the fluid and I'll be back soon for a permanent fix.
I would also like to know exactly what they replaced for your brakes. OEM pads are $120 - $130 installed at my local dealer. I would expect cheaper in the US. Is this the first time your front brakes have been replaced?
I do allot of driving and usually end up needing to change my oil every 6 weeks or so. Since I do it myself, I usually take the extra time and give the truck a once over for other issues. 95% of the time I have the problem diagnosed beforehand and just drop it off at the dealer and tell them what to fix.